Each day a different image or photograph is featured, with an
accompanying caption, which deals with various topics in Earth Science.

Partial Lunar Halo

The above photo showing a lunar halo was taken from Svalboviken, Sweden on February 5, 2004. Lunar halos and simple digital cameras aren't necessarily made for each other. Most digital cameras on the market don't allow shutter speeds long enough to capture the halo phenomenon, and if they do, you end up with a halo that barely fits in the picture. So, since I have a rather simple camera, this is a fortuitous shot of a portion of a 22 degree lunar halo.

The Moon was nearly full on this evening, and a lot of low altitude clouds passed above me, but once these clouds departed, a halo could be observed. Only the left half of the halo is visible on the photo (appearing to nip the tallest tree in the foreground). Halos can occur if hexagonal plate or column crystals in high altitude, cirrus-type clouds are more or less randomly oriented. Moonlight (in this case) enters one side of a crystal, is refracted, and then exits the opposite side, where it is again refracted by the same amount and in the same direction as the original refraction.